A high resolution photoionization study of Ne and Ar: Observation of mass analyzed threshold ions using synchrotron radiation and direct current electric fields

Using the high resolution vacuum ultraviolet (vuv) photon source provided by the monochromatized undulator synchrotron radiation of the Chemical Dynamics Beamline at the Advanced Light Source, we have measured the photoionization efficiency (PLE) spectrum for Ne in the energy range of 21.56-21.67 eV at a wavelength resolution of 0.3 meV [full width at half-maximum (FWHM)]. The PIE spectra for Ne obtained using 0.76 and 2.4 V/cm electric fields reveal autoionizing features attributable to the Rydberg slates Ne[2p(5)ns'(1/2)(1); n = 14-29] and Ne[2p(5)nd'(3/2)(1); n = 12-35] converging to the spin-orbit excited Ne+(P-2(1/2)) state. The positions of these Rydberg states are compared to previous experimental results and those calculated using the quantum defects and IE for Ne+(P-2(1/2)) given in Moore [Natl. Stand Ref. Data Ser. Natl. Bur. Stand. 35 (1971)]. We have also observed mass analyzed threshold ions (MATI) for Ne formed in the Ne+(P-2(3/2,1/2)), states. For Ar, only the MATI peak for Ar+(P-2(3/2)) is observed. The failure tu observe the MATI peak for Ar+(P-2(1/2)) is attributed to shorter lifetimes of high-n Ar[3p(5)ns'(1/2)(1)] and Ar[3p(5)nd'(3/2)(1)] Rydberg stales compared to the minimum time required for separating the prompt Ar+ ions from the field ionized Ar+ ions in this experiment. The MATI peaks for Ne+(P-2(3/2,1/2)) achieves a resolution of 0.7 meV (FWHM). These MATI spectra for Ne and Ar reported here represent the first such studies made using a cw vuv Light source and de electric fields. (C) 1996 American Institute of Physics.